Neoproterozoic 'snowball Earth' simulations with a coupled climate/ice-sheet model

Ice sheets may have reached the Equator in the late Proterozoic era (600-80 0 Myr ago), according to geological and palaeomagnetic studies, possibly re sulting in a 'snowball Earth'. But this period was a critical time in the e volution of multicellular animals, posing the question of how early life su rvived under such environmental stress. Here we present computer simulation s of this unusual climate stage with a coupled climate/ice-sheet model. To simulate a snowball Earth, we use only a reduction in the solar constant co mpared to present-day conditions and we keep atmospheric CO2 concentrations near present levels. We rnd rapid transitions into and out of full glaciat ion that are consistent with the geological evidence. When we combine these results with a general circulation model, some of the simulations result i n an equatorial belt of open water that may have provided a refugium for mu lticellular animals.